1. Technical Field
The present invention relates to a method for manufacturing outlet nozzles for use in rocket engines.
2. Background of the Invention
During operation, a rocket nozzle is subjected to very high stresses, for example in the form of a very high temperature on its inside (on the order of magnitude of 980xc2x0 F.) and a very low temperature on its outside (on the order of magnitude of xe2x88x92370xc2x0 F.). As a result of this high thermal load, stringent requirements are placed upon the choice of material, design and manufacture of the outlet nozzle. At a minimum, the need for effective cooling of the outlet nozzle must be considered.
Cooling is normally provided by attaching individual lengths of tubing on the inside surface of the nozzle. The geometry of each tube is such that it must conform to the conical or parabolic shape of the nozzle. Additionally, the entire inside surface of the nozzle must be covered to prevent xe2x80x9chot spotsxe2x80x9d which could result in premature failure of the nozzle. Each nozzle typically has a diameter ratio from the aft or large outlet end of the nozzle relative to the forward or small inlet end of the nozzle ranging from 2:1 to 3:1.
According to a previously known method of manufacturing a cooled outlet nozzle, rectangular tubes of constant cross section made from nickel-based steel or stainless steel are utilized and arranged parallel with another, and are welded together. The tubes are helically wound such that they form an angle of helix in relation to the longitudinal axis of the nozzle, which angle increases progressively from the inlet end of the nozzle to its outlet end, thereby forming a bell shaped nozzle wall. Rocket engine exhaust flowing along the inside surface of such a nozzle with these helically arranged tubes results in an angled reaction force that induces a roll momentum on the rocket and which must be compensated for by some additional means. These additional means often lead to increased weight and increased flow resistance. Moreover, the spiral winding means that the cooling ducts are long and hence give rise to an increased pressure drop in the flow of cooling medium.
A further method for manufacturing a rocket nozzle is described in patent document WO 00/20749. According to this method, an outer wall is positioned around an inner wall and a plurality of distancing elements are positioned between the inner wall and the outer wall. Finally, the distancing elements are joined to the walls. The distancing elements may also be integrated with the inner wall, for instance, by means of milling the inner wall. In this manner, the cooling channels may be parallel to the longitudinal axis of the nozzle. With this method, it is difficult to vary the cross sectional area of the cooling channels in the longitudinal direction to obtain the desired diameter ratio. To overcome this, the nozzle must be built in several sections in the axial direction.
An objective of the present invention is to provide an improved method for manufacturing a cooled outlet nozzle for a rocket engine.
This is achieved by providing a plurality of preprocessed profile members, each having a web and flanges protruding from said web. Each profile member is milled to present a longitudinally gradually tapering width. The members are curved to conform with the wall section of the nozzle and are joined the members by welding the flanges to form a bell-shaped nozzle structure with cooling channels formed by adjacent webs and adjacent pairs of flanges.
Utilizing such a method enables a rocket engine nozzle to be manufactured that presents high pressure capacity, a low coolant pressure drop, and a long cyclic life, as well as advantageous area ratio.